This application claims the priority benefit of Taiwan application serial no. 88111924, filed Jul. 14, 1999, the full disclosure of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to a fabrication method for a dielectric material with a low dielectric constant. More particularly, the present invention relates to a fabrication method of a low dielectric constant nanotube, which can be used in a damascene process.
2. Description of the Related Art
As the semiconductor technology enters the deep sub-micron territory, the device density continues to increase. As a result, in the design for the multi-level metal interconnects, the continuous increase of the metal conductive layer causes a RC delay in the signal transmission between the metal interconnects and becomes the major factor limiting the transmission speed of the device. To reduce the time delay in the signal transmission, a low resistance material and a low capacitance material are being produced. Since a capacitance is directly proportional to the dielectric constant of the dielectric material, the research and development of materials with a low dielectric constant is the current trend in the semiconductor industry.
The low dielectric constant materials in general can be divided into inorganic and organic type of compounds. The most commonly known low dielectric inorganic material includes fluorine-doped silicon glass (FSG), hydrogen silesquioxiane (HSQ) and methyl sequioxane (MSQ). The fluorine concentration in FSG is difficult to control and, hence, easily leading to moisture absorption and an increase of the dielectric constant. A metal plug poisoning is likely to occur in the subsequent metal plug formation, resulting in an extremely high contact resistance. Since the HSQ consists of hydroxyl (OH) groups in its chemical structure, it absorbs moisture readily, causing a current leakage and an increase of the dielectric constant. To correct the hygroscopic property of the HSQ, the hydroxyl groups (OH) are often replaced with the methyl groups (CH3). The problem of hygroscopicity is resolved by the replacement with the methyl groups; however, the thermal stability is still limited.
In order to increase the speed of signal transmission, besides using a low dielectric constant material for the inner metal dielectric layer, it has become popular to use a low resistance copper for the conductive line. However, various issues arise in the dry etching of copper. For example, if the free radicals of the organic molecules are used to dry etch the copper, the free radicals from the organic molecules easily polymerize to form high molecular weight molecules and adhere on the copper surface, which would interfere the etching process. If ligand molecules, such as 1,1,1,5,5,5-hexafluoroacetylacetonate (hfac) which forms a volatile complex molecule with copper, is used to etch the copper, the etching reaction and the chemical vapor deposition reaction of copper are the forward and the reverse reactions. During the etching of copper is thereby often accompanied by the deposition of copper. If the reversible reaction is not in equilibrium and the ligand molecules are more reactive with copper, an undercut is formed in the underlying copper of the photoresist. Even when the temperature is raised to increase the volatility of the copper-ligand complex molecule, the dielectric layer can be easily damaged if the dielectric layer is a thermally unstable organic low dielectric constant material. It is, therefore, damascening is still the major approach in the copper conductive line technology.
The present invention provides a fabrication method for a non-selective nanotube thin film layer. The method includes forming a catalytic layer on the substrate followed by the formation of a nanotube layer on the catalytic layer by chemical vapor deposition.
The present invention provides a fabrication method for a selective nanotube thin film layer. The method includes forming a catalytic layer on the substrate followed by patterning the catalytic layer. A nanotube layer is then formed on the patterned catalytic layer by chemical vapor deposition.
The present invention provides another fabrication method for a selective nanotube thin film layer. This method includes forming a patterned photoresist layer on the substrate, followed by the formation of multiple catalytic layers on the photoresist layer and on the exposed substrate respectively. The photoresist layer and its overlying catalytic layer are then removed to form a nanotube layer on the remaining catalytic layer on the substrate by chemical vapor deposition.
The present invention provides a damascene process performed on a nanotube. The method includes the formation of a catalytic layer on the substrate, followed by patterning the catalytic layer. A nanotube layer is formed on the patterned catalytic layer by chemical vapor deposition. A conformal barrier layer is then formed on the substrate, followed by filling the openings in the nanotube layer on the substrate with a metal conductive layer.
The present invention provides another damascene process conducted on a nanotube layer. The method includes forming a patterned photoresist layer on the substrate followed by forming multiple catalytic layers on the photoresist layer and on the exposed substrate respectively. The photoresist layer and its overlying catalytic layer are removed. A nanotube layer is then formed on the remaining catalytic layer on the substrate by chemical vapor deposition. Thereafter, a conformal barrier layer is formed on the substrate, followed by filling the openings in the nanotube layer on the substrate with a metal conductive layer.
The materials for the above substrate includes single crystal silicon, III-V groups semiconductors, glass or quartz. The catalytic layer includes iron, colbalt, nickel, gold or platinum types of metal. Materials for the nanotube layer include carbon or boron nitride. The carbon nanotube is formed by chemical vapor deposition using the deposition gases of hydrocarbon compound/H2/nitride containing compound/SiH4 at the approximated flow rates of 16-24 sccm, 64-96 sccm, 64-96 sccm and 3-5 sccm respectively. The gas sources of the chemical vapor deposition process for the boron nitride nanotube include B2H6/N2, B2H6/NH3 or B(OCH3)3/N2/H2.
According to the present invention, using a nanotube for a dielectric layer results in low dielectric constant because of the existence of pores throughout the structure of the nanotube. The nanotube also has good thermal stability because it does not absorb moisture easily due to the low polarity of the nanotube wall. The formation of the dielectric layer with a nanotube therefore stabilizes the quality of the dielectric layer. In addition, a nanotube dielectric layer can be directly formed by patterning a catalytic layer or by forming a catalytic layer on a patterned photoresist layer and on a substrate, followed by removing the photoresist layer and its overlying catalytic layer. The patterned nanotube layer can also be used for the damascene process, which is highly beneficial in the manufacturing of a copper conductive line. Especially using the patterned photoresist layer to directly form a patterned nanotube layer followed by a damascene process, multiple metalizing processes can be conducted without any etching of the dielectric layer or the metal.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.